REVEALED: How Humphrey Bogart snubbed Ingrid Bergman on set of Casablanca

Bogart also blanked Bergman on set, often failing to even acknowledge her presence until the cameras began rolling and they had to shoot some of the iconic romance scenes.

Film historian Noah Isenberg revealed the tortured reality behind the making of a cinema classic in his book We’ll Always Have Casablanca – released to coincide with the 75th anniversary of the film’s premiere in 1942.

At the time Bogart “had generally played gun-toting gangsters and private dicks”, while Swedish-born Bergman had made only a handful of films and was not yet a household name.

He added: “Casablanca gave her the chance to display fully her talent for restrained, demure European sophistication – a kind of understated eroticism.”

The script of the film also launched enduring catchphrases like “Here’s looking at you, kid,” “We’ll always have Paris,” and “Play it, Sam,”.

But despite their on-screen magic making the movie became an off-screen nightmare because of Bogart’s boorish behaviour.

Mr Isenberg said: “He was going through a nasty period with his wife – actress Mayo Methot – and there were a lot of gin-fuelled rages.”

Bergman’s suggestions that they try to bond on dinner dates were all either turned down or simply ignored by Bogart, who stormed off drunkenly on one occasion to play solo chess instead.

Mr Isenberg added that most times the cameras weren’t rolling, “he kept to himself, playing chess in his trailer”.

The actor was forced to later concede that Casablanca “catapulted them both to international superstardom”.

Mr Isenberg added: “He said the moment Ingrid kissed him, he became a romantic lead. That was the pixie dust that needed to be sprinkled over him.”

The book also revealed that the song As Time Goes By – written by Herman Hupfeld in 1931 – almost didn’t make the cut because soundtrack composer Max Steiner at first “hated the idea of using someone else’s schmucky song”.